1. Field of the Invention
The present invention relates to a plasma etching method and a storage medium, and more particularly to a plasma etching method in which a CwFx (x and w are predetermined natural numbers)-based low-dielectric insulating film and a stop layer that stops etching are exposed to plasma at the same time.
2. Description of the Related Art
In recent years, in a semiconductor device manufactured from a semiconductor wafer through a CVD process or plasma etching, a low-dielectric insulating film is used so as to lower parasitic capacitance due to insulation films between wires, and also, copper wiring is used so as to lower wiring resistance. In particular, as a low-dielectric insulating film, for example, a porous SiO2 film, SiOC film, or SOG (Spin on Glass) film (for example, a film formed of hydrogen silsesquioxane (HSQ) or methyl silsesquioxane (MSQ)) is used.
A SiC layer or a SiCN layer is formed as a stop layer on copper wiring so as to prevent inadvertent etching of the copper wiring. When a via hole that reaches the copper wiring is to be formed, these stop layers are removed through etching. In etching of the stop layer, plasma generated from a mixed gas containing a fluorine compound gas (for example, CF4 gas) has been conventionally used (see e.g. Japanese Laid-Open Patent Publication (Kokai) No. 2002-110644 and Japanese Laid-Open Patent Publication (Kokai) No. 2005-303191).
An SOG film is a film that is formed by coating a fluid material and ensures a low dielectric constant by increasing porosity, and therefore, the SOG film has the problem of having a low mechanical strength. Thus, in recent years, it has been considered that a CwFx-based organic film is used as a low-dielectric insulating film having a high mechanical strength.
However, if a CwFx-based organic film is used as a low-dielectric insulating film, when a stop layer such as a SiC layer is etched using plasma generated from CF4 gas, the low-dielectric insulating film is etched at substantially the same etch rate as the etch rate at which the stop layer is etched. For this reason, there is the problem that the selection ratio of the stop layer to the low-dielectric insulating film cannot be increased, and hence the shapes (in particular, depths) of trenches formed in the low-dielectric insulating film cannot be properly adjusted.